1. Field of the Invention
This invention relates to an ignition apparatus for an internal combustion engine in which a capacitor forming a resonance circuit is connected to a coil wound around a core opposite to a signal rotor to effect the detection of ignition timing by means of a change in the oscillation state.
2. Background Art
A previous apparatus of the type referred is shown in FIG. 1.
In the Figure, reference numeral (1) designates a signal generator unit disposed in a distributor (not shown), which unit includes a signal rotor (1a) rotated on a rotary shaft (1a') in synchronism with an internal combustion engine (not shown), a core (1b) opposite the signal rotor (1a) and a coil (1c) wound around the core (1b). Reference numeral (2) is an electronic circuit unit disposed separately from the signal generator unit and including a capacitor (2a) forming a resonance circuit with the coil (1c), an oscillation energy supply circuit (2b) for supplying oscillation energy to this resonance circuit, an oscillation detecting circuit (2c) for detecting the oscillation status of said resonance circuit, an amplifying circuit (2d) for amplifying an output signal from the oscillation detecting circuit (2c), a power transistor (2e) driven with an output from the amplifying circuit (2d), and an electric source circuit (2f). Reference numeral (3) designates an ignition coil which includes a primary winding (3a) and a secondary winding (3b), and reference numeral (4) designates a battery.
The operation is described as follows. The signal rotor (1a) is rotated in synchronism with the internal combustion engine not shown to change the opposition of the core (1b) opposite the signal rotor (1a) to metallic portions on the signal rotor (1a) as shown in FIG. 2(a). On the other hand, the coil (1c) is wound around the core (1b) and the capacitor (2a) is connected to this coil (1c) to form the resonance circuit.
Supplied to this resonance circuit is oscillation energy from the oscillation energy supply circuit (2b) and in the state in which the opposition to the metal is absent as shown in FIG. 2(a), said resonance circuit has developed thereon a suitable oscillation waveform at an amplitude at which a loss of said resonance circuit is balanced with energy supplied by the oscillation energy supply circuit (2b) on the corresponding portion of FIG. 2(b). Also in the state in which the circuit is opposite to the metal, the metal exists in a magnetic path of a magnetic flux generated in the core (1c) and therfore due to a loss within the metal (the greater part of which is an eddy current loss and hysteresis loss), said oscillation is weak and finally results in its stoppage. As a result, said oscillation waveform presents a change as shown in FIG. 2(b). The oscillation detecting circuit (2c) always receives the oscillation waveform shown in FIG. 2(b) and, if the oscillation amplitude becomes larger than a comparison voltage as shown in FIG. 2(b), an output signal is generated as shown in FIG. 2(c). This output signal is amplified by the amplifying circuit 2(d) and drives the power transistor (2e). As a result, a current shown in FIG. 2(d) flows through the primary winding (3a) of the ignition coil (3), and upon interrupting this current, a high amplitude pulse voltage is generated as shown in FIG. 2(e ). The secondary winding (3b) boosts the pulse voltage to provide a high voltage ignition pulse.
Since conventional ignition apparatuses are constructed as described above, it is required to connect the signal generator unit (1) to the electronic circuit unit (2) through leads having sufficient lengths. Because the oscilation waveform shown in FIG. 2(b) is of a high frequency in order to increase the response, there have been the disadvantages that the radiation of unnecessary electric waves is caused from said leads, the high voltage ignition pulses are induced on said leads resulting in the occurrence of malfunction, connecting portions become reduced in reliability, and so on.